In the past, various methods and devices have been used in an attempt to efficiently and economically achieve a reliable soldered electrical connection between two electrically conductive elements. The most common of these methods has been to first strip any insulation from the conductors at the place where soldering is to take place, place the bared portions of the conductors in physical contact with each other and then apply sufficient heat to melt a solder and to remove the oxides from the conductors so as to form an electrical connection.
The insulation may be of any of the conventional types known in the art, including polyethylene, polyethylene with a mixture of nylon, polyesters, oleo films or paper. Many of these materials, and particularly the synthetic ones, are applied as coatings to the conductor which can be, for example, a lead wire. The insulation may be removed from the portion of the conductor which is to be soldered in a variety of ways, the most common being cutting the insulation and physically stripping it from the conductor. Other methods, such as are described in U.S. Pat. No. 3,527,138, include etching the insulation away with chemicals, or melting it with an induction-heated rotary tool. The patent also discloses removal of the insulation by air abrasion through the use of fine aluminum grits, rotary "cookie" cutters, or machine-operated spot facers. Micro-torches have also been used to remove insulation from a large, flat conductive surface; however, this procedure requires multiple passes with the flame to remove all of the insulation.
Several methods for making an electrical connection between two conductors once they have been stripped are also known. U.S. Pat. No. 2,250,156 discloses physically crimping or welding a conductive metal sleeve around two conductors, with or without insulation, to maintain the conductors in electrical contact. U.S. Pat. Nos. 3,314,582 and 3,384,283 use ultrasonic vibrations, without any solder, to form a bond between two conductors.
The previously known methods and apparatus for soldering two conductors, particularly where one is a terminal around or on which a lead wire is to be crimped or wrapped, have distinct disadvantages, especially for high-speed soldering. The apparatus of U.S. Pat. Nos. 3,314,582 and 3,384,283 are bulky, slow and expensive and have limited application to soldering other than miniature components. The sleeve-type devices are also bulky, slow and relatively expensive to apply, and may cause physical damage to the electrical conductors, thereby possibly creating weak spots, high resistivity points or poor electrical connections. The conventional soldering technique of using a hot soldering iron to melt solder to form a connection is also relatively slow and inefficient. In addition, a soldering iron must generate large amounts of heat, in the order of 700.degree. F, so as to "wet" or remove the oxides from the conductors produced when the insulation is put on the conductor, so that the solder bond can be made. This heat may damage the insulation of other conductors in close proximity to the conductors to be joined or may damage electrical components adjacent or attached to the conductors. The high heat generated by the soldering iron also causes substantial amounts of impurities, or "scum" to form in the solder, creating the possibility of an imperfect electrical connection. These impurities form due to the creation of the oxides of the soldering compositions.
A further disadvantage of the previous soldering methods is that they do not lend themselves to high speed assembly line production.
It is therefore an object of this invention to provide a method and apparatus for producing an electrical connection between two or more electrical conductors that is rapid and efficient and produces reliable connections.
A further object is to provide a soldering method that is simple and inexpensive and does not require bulky equipment.
Another object is to provide a method and apparatus for soldering that permits soldering to be performed at lower temperatures than previously available, thereby preventing unnecessary damage to insulation or components.
An additional object is to provide a method and apparatus for preventing residue or scum from the soldering composition from forming during the joinder of conductors.
An additional object is to provide a method and apparatus for soldering that lends itself for use on an assembly line.
Another object is to provide a method and apparatus for soldering that reduces the possibility of physical damage to the conductors being joined and adjacent component.
Finally, another object is to provide a method of soldering that removes oxides or impurities from the conductive surfaces prior to joinder to form more reliable connections.
In accordance with the practice of the invention, an electrical conductor with an insulational film is wrapped around either an electrical terminal post or another conductor. The open flame from a torch is then used to melt the insulation from the insulated conductor at a selected area. The bared portions of the two conductors are then immersed in a heated ultrasonically agitated liquid solder bath to form the soldered connection. The temperature of the liquid solder bath can be kept low, for example, at 400.degree. F. This minimizes the possibility of damage and also reduces the formation of oxides which adversely effects the reliability of the solder joint.
For a better understanding of the present invention together with other and further objects thereof, reference is made to the following description taken in connection with the accompanying drawings, and the scope of the invention will be pointed out in the appended claims.